In normal adult rat liver albumin is synthesized on polysomes attached to the membranes of the rough endoplasmic reticulum. Preliminary evidence indicates that albumin is first produced as a larger precursor protein with a leucine-rich peptide extension at its N-terminal end. The nascent albumin is then vectorially discharged from membrane-attached polysomes and commences on an intracellular path which eventually leads to its secretion. In some Morris minimal deviation hepatomas (5123C, 7800 and 7777) the above description does not hold. In these altered cells albumin is synthesized on free polysomes, rather than on membrane-attached polysomes, and these cells (5123C) cannot secrete albumin. In order to define the biochemical abnormalities which permit this aberrant behavior, we shall determine whether the precursor albumin produced by these hepatomas is different to that produced by normal liver and whether the rough endoplasmic reticulum membranes of the hepatomas lack effective binding sites for albumin polysomes.